#include <bits/stdc++.h>
using namespace std;

#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)
#define SZ(a) int(a.size())
#define ALL(a) a.begin(), a.end()
#define RALL(a) a.rbegin(), a.rend()
#define PB push_back
#define MP make_pair
#define F first
#define S second

typedef long long ll;
typedef double db;
typedef vector<int> vi;
typedef vector<long long> vll;
typedef vector<double> vd;
typedef pair<int, int> pii;
typedef pair<long long, long long> pll;
typedef vector<pair<int, int>> vpii;
typedef vector<pair<long long, long long>> vpll;
typedef set<int> si;
typedef set<long long> sll;
typedef map<int, int> mii;
typedef map<long long, long long> mll;

constexpr int INF = 1e9 + 47;
constexpr long long LINF = (ll)1e18 + 4747;
constexpr int MOD = 998244353;
constexpr int N = 1e6 + 47;


int main()
{
    ios_base::sync_with_stdio(false);
	cin.tie(nullptr);

	int n, k;
	cin >> n >> k;
	vector a(n, vi(2, 1));
	string str;
	cin >> str;
	FOR (i, 0, n)
	{
		if (str[i] == 'L')
			a[i][1] = 0;
		else
			a[i][0] = 0;
	}

	int f = 0;
	pii pos = { 0, 0 };
	while (pos.F != n)
	{
		if (a[pos.F][pos.S] == 0)
		{
			f++;
			pos.S = (pos.S + 1) % 2;
		}
		else
		{
			pos.F++;
			pos.S = (pos.S + 1) % 2;
		}
	}

	cout << max(0, k - f) << '\n';

    return 0;
}